|Publication number||US7015991 B2|
|Application number||US 10/302,405|
|Publication date||Mar 21, 2006|
|Filing date||Nov 21, 2002|
|Priority date||Dec 21, 2001|
|Also published as||CN1605041A, CN100380194C, EP1456714A1, EP1456714A4, US20030117546, WO2003058339A1|
|Publication number||10302405, 302405, US 7015991 B2, US 7015991B2, US-B2-7015991, US7015991 B2, US7015991B2|
|Inventors||Arlie R. Conner, Gary B. Kinglsey|
|Original Assignee||3M Innovative Properties Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Non-Patent Citations (1), Referenced by (6), Classifications (18), Legal Events (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of Provisional Application No. 60/343,105, filed Dec. 21, 2001.
An illumination system 12 with a light source 14 provide uniform illumination of an multi-color liquid crystal display (LCD) 16, which has embedded color filters 18R, 18G, and 18B corresponding to red, green and blue primary color components. Color filters 18R, 18G, and 18B are aligned over individual sub-pixels (not shown) of LCD 16.
Each subpixel is independently addressable so that the liquid crystal molecules of LCD 16 can be driven to certain tilt angles as is known in the art, to effect varying degrees of light transmission intensity. With appropriate associated polarizers, for example, this varies the red, green and blue subpixel intensities to provide a generally full color image. Projection optics 20, which are represented schematically, project the color image to a display screen 22.
Problems with this brute force approach are a low transmission rate, especially when color filters are highly saturated, so as to yield good (i.e. pure) color primaries, or poor color saturation (yielding impure color primaries) to increase transmission rate. In addition, this approach also causes heating within the LCD panel due to absorption by the color filters. Typically, the absorption of green light by the red color component filter 18R is inevitable. Likewise, a blue color component filter 18B passes mainly just blue light and green filter 18G passes mainly just green light. Thus the majority of the illumination light (i.e., ⅔ of total) is absorbed by the color component filters 18R, 18G, and 18B. Simplified diagrams of light spectra illustrate generally a spectrum 30 for polychromatic (“white”) light provided by light source 14 and the resulting spectra 32, 34, and 36 of respective red, green, and blue color components generated by projection system 10.
The present invention addresses all three of these problems, by providing a color prefilter, positioned between the light source and the LCD panel, to shape the spectrum of the illumination so as to increase the relative panel transmission and to reduce the heat absorption within the LCD embedded color filters.
The present invention includes a single-panel LCD projection system that includes a color prefilter positioned between an illumination system and a multi-color liquid crystal display (LCD) having an associated polarizer and analyzer. The color prefilter functions to shape the spectrum of illumination provided by the illumination system so as to increase relative panel transmission and to reduce heat absorption by color component filters (e.g., red, green and blue) incorporated in the LCD.
The color prefilter is selected to eliminate from or greatly reduce in the illumination light the intensity of certain wavebands that do not materially contribute to generating pure primary colors. A consequence of adding the color prefilter is that the LCD color component filters can be desaturated and the overall total transmission of the projection system can be improved. In one implementation, the color prefilter is able to remove the wavebands of highest absorption by the LCD color component filters before such light strikes the LCD, so that there is less heat build-up in the LCD.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.
Prefilter 52 is selected to eliminate from or greatly reduce in the illumination light the intensity of certain wavebands that do not materially contribute to generating pure primary colors. A consequence of the filtering provided by prefilter 52 is that the LCD color filters 58 can be desaturated, and the overall total transmission of projection system 50 can be improved. In one implementation, the prefilter 52 is able to remove the wavebands of highest absorption by color component filters 58 before such light strikes the LCD 56, so that there is less heat-up in the LCD 56.
The prefilter 52 shapes the light spectrum from illumination system 54 source into distinct red, green, and blue subbands. Hence prefilter 52 is configured to have steep transmission edges around two notches, located around 500 and 590 nm regions of the visible spectrum (commonly specified as 400 to 700 nm). Color purity for red, green, and blue primaries can be arbitrarily improved by increasing the prefilter notch bandwidths. A simplified diagram of a spectrum 64 of polychromatic light provided to LCD 56 with chromatic “notches” 66 and 68 that illustrate the filtering or blocking of respective cyan and yellow color components by prefilter 52.
When a conventional color filtered LCD 16 is used for projection, most of the illuminating light is absorbed by the color filter matrix 18. Even with high transmission type color filters 18, the LCD panel 16 passes only about 16% of the light that passes through the incident polarizing filter. This transmission is characteristic of a LCD panel 16 that operates in a twisted nematic mode and in which the liquid crystal cell is sandwiched between an incident polarizer and an outgoing analyzer.
With reference to prior art projection system 10 of
In order to portray television signals, the color primaries can be observed by analyzing the sub-channel spectra may be represented as:
Each of color filters 18R, 18B, and 18G can in theory be darkened until it gives sufficient color purity so that specified primary red, green, and blue colors specified by SMPTE (Society of Motion Picture and Television Engineers) for HDTV can be projected onto display screen 22. For example, the dyestuff or pigment used for color filters 18 can be concentrated or layered in thicker fashion during fabrication to allow such highly saturated primary colors, but such purity will be accompanied by a strong loss of transmissivity. An equally problematic consequence of such color-enhanced filters is a significant absorption of the illumination power, which will lead to heating of the color filter layer 18 and the entire LCD 16.
It is difficult to remove such heat from the glass substrates of the LCD 16—because glass is not a very good thermal conductor. As a result, some residual problems can remain. U.S. Pat. No. 5,682,216 describes use of a plastic film made of TAC (Tri-Acetyl Cellulose) to reduce or eliminate thermals from showing up as image artifacts.
In this context, the positioning of prefilter 52 in front of LCD 56, and lighter color filters 58, can help reduce heating of the LCD 56. Table 1 below compares such a projection system 50 with a prefilter 52 and lighter color filters 58 with the prior art projection system 10 (with conventional color filters and no prefilter).
This Invention, with prefilter
using 2 notches
x = 0.65
x = 0.65
y = 0.34
y = 0.33
x = 0.31
x = 0.30
y = 0.65
y = 0.63
x = 0.15
x = 0.16
y = 0.07
y = 0.07
x = 0.29
x = 0.29
y = 0.34
y = 0.34
Table 1 illustrates that nearly ideal color primaries can be obtained with either system. Both systems are based on commercially available color filters and a Philips UHP 100 W lamp. Equally good color primaries are obtained with the prefiltered (double-notch filtered) UHP source and lighter color filter set. There is an improvement in overall transmission for the prefiltered system of approximately 5%.
The prefiltered panel absorbs 78% of the prefiltered illumination energy, whereas the conventional system with nonfiltered source has the LCD absorbing 84% of the illumination. Moreover, the prefilter causes a reduction of light incident at the LCD of about 25%, so that the amount of optical power absorbed by the LCD with lighter color filter set is reduced to (78*75=) 58.5% of the original lamp's power. Not only is the prefiltered system brighter, but the absorbed energy in the LCD is reduced to only about 75% of that for the nonfiltered system.
The notch filters 52A and 52B can be made as two independent layers or devices for easier angle-tuning in mass production, or if sufficient repeatability can be had, combined as a single prefilter unit 52 for a lower parts count and slightly higher transmission due to elimination of surfaces. Angle-tuning refers to sensitivity that interference filters have with angle of incidence. We can simply tilt the filter 5 to 15 degrees to adjust the notch band (toward the blue with increasing angle). In one implementation, filters 52A and 52B may be formed to be oriented at an angle of incidence 96 (
Other degrees of freedom are also available for perfecting the color primaries with the prefiltered projection system 50. Although the edges of the notches 66 and 68 (
The prefiltered projection system 50 allows a designer to treat saturation of embedded color filters 58 as a variable in which one can individually densify or lighten the saturation of color component filters 58R, 58G, 58B. At the same time one can also design the prefilter 52 to narrow or widen the two notch regions 66 and 68 and adjust placement of all four of the notch edges. By iterating one can find optimal transmission for the entire system, lessened absorption in the color filters 58, and precise RGB color points as specified by display or television standards (e.g., SMPTE HDTV)
The typical light source for projection TV is a high pressure mercury discharge lamp, which has a known deficiency in red wavelengths and strong peak in mid-green region, at 546 nm. The embodiment of
In one implementation, prefilters 52A and 52B are made from holographic materials, dichromated gelatin (DCG), due to excellent edge characteristics and low cost. Furthermore such DCG materials have excellent reliability and performance with strong light incidence. Preferably there is a UV rejection filter placed immediately ahead of the prefilter 52 to practically eliminate damaging ultraviolet light.
Prefilter 102 functions in a manner analogous to that of prefilters 52 (
Transmissive notch filters 52 omit undesired yellow and cyan light components by reflecting them away from the LCD 56. By selectively reflecting tuned red, green and blue light components toward the LCD 110, reflective triple band prefilter 102 omits undesired yellow and cyan light components by absorbing them or transmitting them away from LCD 110. As a result, reflective triple band prefilter 102 increases relative panel transmission and reduces heat absorption by color component filters 112 incorporated in LCD 110 in the manner described above for transmissive notch filters 52. An aspect of single-panel LCD projection system 100 is that color-tuned reflective filters, such as reflective triple band prefilter 102, can be easier to manufacture than color-tuned transmissive notch filters, such as transmissive notch filters 52.
Projection system 120 is substantially the same as projection system 100, except that except the former substitutes a concave substrate for collimating lens 106 to provide convergence of color-tuned illuminating light directed to LCD 130. Projection optics 134, represented schematically, project a display image to a display screen 136.
For example, PCS 160 includes a supported dielectric film 162 that is polarization selective and generally achromatic. One of S- and P-polarized light is transmitted through dielectric film 162 (e.g., S-polarized light), and the other of the S- and P-polarized light (e.g., P-polarized light) is reflected to a dielectric film 164 on an adjacent inclined face of a prism 166 to be reflected outward through a half-wave retarder 168. Half-wave retarder 168 converts the reflected S-polarized light to P-polarized light, so that all light passing from PCS 160 is of a single polarization (e.g., S-polarization).
Reflective triple band prefilter 152 may be formed of gradient filters that preferentially reflect the primary color components red, green, and blue at, for example, an angle 170 of 45 degrees from the angle of incidence. In one implementation, a magenta filter may be substituted for the red and blue gradient filters to form the equivalent of a double-notch filter. In either implementation, the gradient filters may be formed on separate substrates or on a common substrate. Prefilter 152 reflects the color-filtered light to a LCD 172 with color component filters 174R, 174G, and 174B, and projection optics 176 project a display image to a display screen 178.
For example, PCS 190 includes a supported dielectric film 202 that is polarization selective and generally achromatic. One of S- and P-polarized light is transmitted through dielectric film 202 (e.g., S-polarized light), and the other of the S- and P-polarized light (e.g., P-polarized light) is reflected to a dielectric film 204 on an adjacent inclined face of a prism 206 to be reflected outward through a half-wave retarder 208. Half-wave retarder 208 converts the reflected S-polarized light to P-polarized light, so that all light passing from PCS 190 is of a single polarization (e.g., S-polarization).
In one implementation, double notch prefilter 182 is formed of a stack of stretch plastic films, each with specific retardation value and each at a specific angle, thereby forming a filter that simply rotates some wavelengths (by 90 degrees ideally) and leaves other wavelengths unrotated (or effectively orthogonal to the other band). Transmissive, optical retarder stack double notch prefilter 182 is commercially available from ColorLink, Inc. of Boulder, Colo. An advantage of the retarder stack double-notch prefilter 182 is that it has a relatively large viewing angle over which there is no substantial shift of the edges of the filter bands.
The configuration of LCD projection system 180, namely the positioning of retarder stack double-notch prefilter 182 between polarization conversion system 190 and polarizer 194, allows retarder stack double-notch prefilter 182 to eliminate or reduce the notched wavebands. Polarizer 194, positioned just substantially adjacent LCD 192 also enhances image contrast of projection system 180. In some implementations of projection system 180, LCD 192 with high accuracy color filters 210R, 210G, and 210B may substitute for retarder stack double-notch prefilter 182 a retarder stack-notch prefilter with only one (e.g., yellow) notchband.
Notch color filter 252 functions to shape the spectrum of illumination provided by the combination of illumination system 254 and LCD 256. Notch color filter 252 is selected to eliminate from or greatly reduce in the illumination light the intensity of certain wavebands that do not materially contribute to generating pure primary colors. A consequence of the filtering provided by notch color filter 252 is that the LCD color filters 258 can be desaturated, and the overall total transmission of projection system 250 can be improved. A disadvantage of the positioning of notch color filter 252 after LCD 256 is that some undesirable wavebands may be absorbed by color component filters 258, thereby resulting in some heating of LCD 256. For example, notch color filter 252 can be formed from holographic materials, dichromated gelatin (DCG), as described above.
Typically an LCD rear-projection system uses a 100 W high pressure mercury lamp which outputs around 6000 lumens and can have a lifetime of at least 10,000 hours, a requirement for home television application. The various embodiments of the present invention may be employed in a variety of projection display applications, including color television rear projection systems and various other front and rear projection systems.
In view of the many possible embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. Rather, I claim as my invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.
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|U.S. Classification||349/106, 349/5, 349/104, 348/E09.027|
|International Classification||G02F1/1335, G02B5/20, G02F1/13357, H04N9/31, G03B21/00, G02B5/22|
|Cooperative Classification||H04N9/3108, G02F2001/133628, H04N9/3158, G02F1/133509|
|European Classification||H04N9/31R5F, H04N9/31A1S, G02F1/1335F, H04N9/31V|
|Nov 21, 2002||AS||Assignment|
Owner name: CORNING PRECISION LENS, INCORPORATED, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CONNER, ARLIE R.;KINGSLEY, GARY B.;REEL/FRAME:013521/0428
Effective date: 20021121
|Feb 18, 2003||AS||Assignment|
Owner name: 3M PRECISION OPTICS, INC., OHIO
Free format text: CHANGE OF NAME;ASSIGNOR:CORNING PRECISION LENS, INC.;REEL/FRAME:013429/0359
Effective date: 20021213
Owner name: 3M INNOVATIVE PROPERTIES COMPANY, MINNESOTA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:3M PRECISION OPTICS, INC.;REEL/FRAME:013429/0259
Effective date: 20030212
|Jul 11, 2006||CC||Certificate of correction|
|Sep 19, 2006||CC||Certificate of correction|
|Oct 26, 2009||REMI||Maintenance fee reminder mailed|
|Mar 21, 2010||LAPS||Lapse for failure to pay maintenance fees|
|May 11, 2010||FP||Expired due to failure to pay maintenance fee|
Effective date: 20100321